The following acronyms may be used throughout the description:
BCCH (Broadcast Control Channel), BCH (Broadcast Channel), BMC (Broadcast/Multicast Control), CB (Cell Broadcast), CCCH (Common Control Channel), CN (Core Network), CRNC (Controlled Physical Channel Reconfiguration), CS (Circuit Switched), CTCH (Common Traffic Channel), DCCH (Dedicated Control Channel), DCH (Dedicated Channel), DPCH (Dedicated Physical Channel), DPDSCH (Dedicated Physical Downlink Shared Channel), DSCH (Downlink Shared Channel), DTCH (Dedicated Traffic Channel), EIR (Equipment Identify Register), FACH (Forward Access Channel), FDD (Frequency Division Combining), GGSN (Gateway GPRS Support Node), GMSC (Gateway Mobile Switching Center), GPRS (General Packet Radio Service), HFN (Hyper Frame Number), HSS (Home Subscriber Server), MAC (Medium Access Control), MBMS (Multimedia Broadcast/Multicast Service), MCCH (MBMS point-to-multipoint Control Channel), MGW (Media Gateway), MIB (Master Information Block), MICH (MBMS Notification Indicator Channel), MSC (Mobile Switching Centre), MSCH (MBMS Scheduling Channel), MTCH (MBMS point-to-multipoint Traffic Channel), OSI (Open System Interconnection), PCCH (Paging Control Channel), PCCPCH (Primary Common Control Physical Channel), PCPICH (Primary Common Pilot Channel), PDCP (Packet Data Convergence Protocol), PDSCH (Physical Downlink Shared Channel), PDU (Protocol Data Unit), PICH (Paging Indicator Channel), PLMN (Public Land Mobile Network), PMM (Packet Mobility Management), PS (Packet Switched), PSTN (Public Switched Telephone Network), PtM (Point-to-multipoint transmission), RAB (Radio Access Bearer), RACH (Radio Access Channel), RAN (Radio Access Network), RAT (Radio Access Technology), RLC (Radio Link Control), RNC (Radio Network Controller), RNS (Radio Network Sub-systems), RRC (Radio Resource Control), SAP (Service Access Point), SCCH (Shared Control Channel), SCCPCH (Secondary Common Control Physical Channel), SDU (Service Data Unit), SFN (System Frame Number), SGSN (Serving GPRS Service Node), SIB (System Information Block), SN (Sequence Number), SRNC (Serving Radio Network Controller), TDD (Time-Division Duplexing), TTI (Transmission Time Interval), UE (User Equipment), UTRAN (UMTS Terrestrial Radio Access), W-CDMA (wideband code division multiple access).
Recently, mobile communication systems have developed remarkably, but for high capacity data communication services, the performance of mobile communication systems cannot match that of existing wired communication systems. Accordingly, technical developments for IMT-2000, which is a communication system allowing high capacity data communications, are being made and standardization of such technology is being actively pursued among various companies and organizations.
A universal mobile telecommunication system is a third generation mobile communication system that has evolved from a European standard known as Global System for Mobile communications (GSM). The UMTS aims to provide improved mobile communication service based on a GSM core network and wideband code division multiple access (W-CDMA) wireless connection technology.
In December 1998, ETSI of Europe, ARIB/TTC of Japan, T1 of the United States, and TTA of Korea formed a Third Generation Partnership Project (3GPP) for creating the detailed specifications of the UMTS technology.
Within the 3GPP, in order to achieve rapid and efficient technical development of the UMTS, five technical specification groups (TSG) have been created for performing the standardization of the UMTS by considering the independent nature of the network elements and their operations.
Each TSG develops, approves, and manages the standard specification within a related region. Among these groups, the radio access network (RAN) group (TSG-RAN) develops the standards for the functions, requirements, and interface of the UMTS terrestrial radio access network (UTRAN), which is a new radio access network for supporting W-CDMA access technology in the UMTS.
FIG. 1 illustrates an exemplary basic structure of a general UMTS network. As shown in FIG. 1, the UMTS is roughly divided into a terminal or user equipment UE 10, a UTRAN 100 and a core network (CN) 200.
The UTRAN 100 includes one or more radio network sub-systems (RNS) 110, 120. Each RNS 110, 120 includes a radio network controller (RNC) 111, and a plurality of base stations or Node-Bs 112, 113 managed by the RNC 111 through an Iub interface. The RNC 111 handles the assigning and managing of radio resources, and operates as an access point with respect to the core network 200. RNCs 111 can be connected together via the Iur interface.
The Node-Bs 112, 113 receive information sent by the physical layer of the terminal 10 through an uplink, and transmit data to the terminal 10 through a downlink The Node-Bs 112, 113, thus operate as access points of the UTRAN 100 for the terminal 10. Each Node-B controls one or several cells, each being characterised by the coverage of a given geographical area on a given frequency.
A primary function of the UTRAN 100 is forming and maintaining a radio access bearer (RAB) to allow communication between the terminal and the core network 200. The core network 200 applies end-to-end quality of service (QoS) requirements to the RAB, and the RAB supports the QoS requirements set by the core network 200. As the UTRAN 100 forms and maintains the RAB, the QoS requirements of end-to-end are satisfied. The RAB service can be further divided into an Iu bearer service and a radio bearer service. The Iu bearer service supports a reliable transmission of user data between boundary nodes of the UTRAN 100 and the core network 200.
The core network 200 includes a mobile switching centre (MSC) 210 and a Media Gateway MGW 220 connected together for supporting a circuit switched (CS) service, and a serving GPRS support node (SGSN) 230 and a gateway GPRS support node 240 connected together for supporting a packet switched (PS) service.
The services provided to a specific terminal are roughly divided into the circuit switched (CS) services and the packet switched (PS) services. For example, a general voice conversation service is a circuit switched service, while a Web browsing service via an Internet connection is classified as a packet switched (PS) service.
Various types of interfaces exist between network components to allow the network components to transmit and receive information to and from each other for mutual communication therebetween. An interface between the RNC 111 and the core network 200 is defined as an Iu interface. Each RNC is connected via the interface Iu to the core network 200. In particular, the Iu interface between the RNCs 111 and the core network 200 for packet switched systems is defined as Iu-PS, and the Iu interface between the RNCs 111 and the core network 200 for circuit switched systems is defined as Iu-CS.
For supporting circuit switched services, the RNCs 111 are connected to the MSC 210 of the core network 200, and the MSC 210 is connected to the Media Gateway (MGW) 220 which manages the connection with other networks via the interface Nb. The MGW 220 may be connected to the Public Switched Telephone Network (PSTN) in order to adapt codecs between the PSTN and the connected Radio Access Network. For supporting packet switched services, the RNCs 111 are connected to the SGSN 230 and the GGSN 240 of the core network 200. The SGSN 230 supports the packet communications going toward the RNCs 111, and the GGSN 240 manages the connection with other packet switched networks, such as the Internet, via the interface Gi. The GGSN 240 notably handles the routing, the charging and the separation of data flows into different Radio Access Bearers RAB. The SGSN is connected via the GS interface to the MSC and via the GN interface to the GGSN. The SGSN 230 is connected by respective interfaces to an EIR and to a HSS (not illustrated). The MSC 210 is connected by respective interfaces to the EIR and the HSS. The MGW 220 is connected by an interface to the HSS. The GGSN is connected by an interface to the HSS. The EIR hosts lists of mobiles which are allowed or not to be used on the network. The HSS handles the subscription data of the users.
FIG. 2 illustrates a structure of a radio interface protocol between the terminal and the UTRAN according to the 3GPP radio access network standards.
As shown in FIG. 2, the radio interface protocol has horizontal layers comprising a physical layer, a data link layer, and a network layer, and has vertical planes comprising a user plane UP for transmitting user data and a control plane CP for transmitting control information.
The user plane is a region that handles traffic information of the user, such as voice or Internet protocol (IP) packets, while the control plane is a region that handles control information for an interface of a network, maintenance and management of a call, and the like.
The protocol layers in FIG. 2 can be divided into a first layer (L1), a second layer (L2), and a third layer (L3) based on three lower layers of an open system interconnection (OSI) standard model. Each layer will be described in more detail as follows.
The first layer (L1), namely, the physical layer, provides an information transfer service to an upper layer by using various radio transmission techniques. The physical layer is connected to an upper layer called a medium access control (MAC) layer, via a transport channel. The MAC layer and the physical layer send and receive data with one another via the transport channel.
The second layer (L2) includes a MAC layer, a radio link control (RLC) layer, a broadcast/multicast control (BMC) layer, and a packet data convergence protocol (PDCP) layer.
The MAC layer handles mapping between logical channels and transport channels. The MAC layer provides an allocation service of the MAC parameters for allocation and re-allocation of radio resources. The MAC layer is connected to an upper layer called the radio link control (RLC) layer, via a logical channel.
Various logical channels are provided according to the kind of transmitted information. In general, when information of the control plane is transmitted, a control channel ctrl is used. When information of the user plane is transmitted, a traffic channel is used. A logical channel may be a common channel or a dedicated channel depending on whether the logical channel is shared. Logical channels include a dedicated traffic channel (DTCH), a dedicated control channel (DCCH), a common traffic channel (CTCH), a common control channel (CCCH), a broadcast control channel (BCCH) and a paging control channel (PCCH) or a Shared Channel Control Channel (SHCCH). The BCCH provides information including information utilized by a terminal to access a system. The PCCH is used by the UTRAN to access a terminal.
A Multimedia Broadcast/Multicast Service (MBMS or MBMS service) refers to a method of providing streaming or background services to a plurality of UEs using a downlink-dedicated MBMS radio bearer that utilizes at least one of point-to-multipoint and point-to-point radio bearer. MBMS is introduced in the UMTS standard in the Release 6 of the specification. It describes techniques for optimised transmission of MBMS bearer service in UTRA such as point-to-multipoint transmission, selective combining and transmission mode selection between point-to-multipoint and point-to-point bearer. This is used in order to save radio resources when the same content is sent to multiple users, and enables TV-like services. One MBMS service includes one or more sessions and MBMS data is transmitted to the plurality of terminals through the MBMS radio bearer only while the session is ongoing.
As the name implies, an MBMS may be carried out in a broadcast mode or a multicast mode. The broadcast mode is for transmitting multimedia data to all UEs within a broadcast area, for example the domain where the broadcast is available. The multicast mode is for transmitting multimedia data to a specific UE group within a multicast area, for example the domain where the multicast service is available.
For the purposes of MBMS, additional traffic and control channels exist. For example, an MCCH (MBMS point-to-multipoint Control Channel) is used for transmitting MBMS control information, an MTCH (MBMS point-to-multipoint Traffic Channel) is used for transmitting MBMS service data and an MSCH is used to transmit scheduling information. The MCCH schedule is common for all services.
The different logical channels that exist are listed below:
For the control channel CCH: BCCH, PCCH, DCCH, CCCH, SHCCH and MCCH. For the Traffic channel TCH: DTCH, CTCH and MTCH.
The MAC layer is connected to the physical layer by transport channels and can be divided into a MAC-b sub-layer, a MAC-d sub-layer, a MAC-c/sh sub-layer, and a MAC-hs sub-layer according to the type of transport channel to be managed.
The MAC-b sub-layer manages a BCH (Broadcast Channel), which is a transport channel handling the broadcasting of system information. The MAC-d sub-layer manages a dedicated channel (DCH), which is a dedicated transport channel for a specific terminal. Accordingly, the MAC-d sub-layer of the UTRAN is located in a serving radio network controller (SRNC) that manages a corresponding terminal, and one MAC-d sub-layer also exists within each terminal (UE).
The MAC-c/sh sub-layer manages a common transport channel, such as a forward access channel (FACH) or a downlink shared channel (DSCH), which is shared by a plurality of terminals, or in the uplink the Radio Access Channel (RACH). In the UTRAN, the MAC-c/sh sub-layer is located in a controlling radio network controller (CRNC). As the MAC-c/sh sub-layer manages the channel being shared by all terminals within a cell region, a single MAC-c/sh sub-layer exists for each cell region. Also, one MAC-c/sh sublayer exists in each terminal (UE). The MAC-m sublayer may handle the MBMS data.
Referring to FIG. 3, possible mapping between the logical channels and the transport channels from a UE perspective is shown. Referring to FIG. 4, possible mapping between the logical channels and the transport channels from a UTRAN perspective is shown.
The RLC layer supports reliable data transmissions, and performs a segmentation and concatenation function on a plurality of RLC service data units (RLC SDUs) delivered from an upper layer. When the RLC layer receives the RLC SDUs from the upper layer, the RLC layer adjusts the size of each RLC SDU in an appropriate manner upon considering processing capacity, and then creates certain data units with header information added thereto. The created data units are called protocol data units (PDUs), which are then transferred to the MAC layer via a logical channel. The RLC layer includes a RLC buffer for storing the RLC SDUs and/or the RLC PDUs.
The BMC layer schedules a cell broadcast message (referred to as a CB message, hereinafter) received from the core network, and broadcasts the CB messages to terminals located in a specific cell(s). The BMC layer of the UTRAN generates a broadcast/multicast control (BMC) message by adding information, such as a message ID (identification), a serial number, and a coding scheme to the CB message received from the upper layer, and transfers the BMC message to the RLC layer. The BMC messages are transferred from the RLC layer to the MAC layer through a logical channel, i.e., the CTCH (Common Traffic Channel). The CTCH is mapped to a transport channel, i.e., a FACH, which is mapped to a physical channel, i.e., a S-CCPCH (Secondary Common Control Physical Channel).
The PDCP (Packet Data Convergence Protocol) layer, as a higher layer of the RLC layer, allows the data transmitted through a network protocol, such as an IPv4 or IPv6, to be effectively transmitted on a radio interface with a relatively small bandwidth. To achieve this, the PDCP layer reduces unnecessary control information used in a wired network, with a function called header compression.
A radio resource control (RRC) layer is located at a lowermost portion of the L3 layer. The RRC layer is defined only in the control plane, and handles the control of logical channels, transport channels, and physical channels with respect to setup, reconfiguration, and release or cancellation of radio bearers (RBs). The radio bearer service refers to a service provided by the second layer (L2) for data transmission between the terminal and the UTRAN. In general, the setup of the radio bearer refers to the process of defining the characteristics of a protocol layer and a channel required for providing a specific data service, as well as respectively setting detailed parameters and operation methods. Additionally, the RRC handles user mobility within the Radio Access Network, and additional services like location services.
The different possibilities that exist for the mapping between the radio bearers and the transport channels are not always possible. The UE/UTRAN deduces the possible mapping depending on the UE state and the procedure that the UE/UTRAN is executing. Different states and modes are explained in more detail below.
The different transport channels are mapped onto different physical channels. For example, the RACH transport channel is mapped on a given PRACH, the DCH can be mapped on the DPCH, the FACH and the PCH can be mapped on the S-CCPCH, the DSCH is mapped on the PDSCH and so on. The configuration of the physical channels is given by an RRC signalling exchange between the RNC and the UE.
In the following description, the start and the reconfiguration of a S-CCPCH carrying MTCH is described. The stop of a service can be considered as a special reconfiguration, i.e. the S-CCPCH has a null configuration.
According to the background art, when the UE reads the configuration of a service which is sent in PtM mode, the UE supposes this configuration is valid immediately. The UE receives the list of services that are active at the moment in one of the two messages; MBMS Unmodified services Information or in the message MBMS Modified services Information. These messages indicate that UEs that want to receive this service should perform a specific action, for example acquire information for counting purposes, acquire information for the configuration of the PtM radio bearer, establish a PMM connection, stop receiving the PtM radio bearer etc. On the network side, when the configuration is changed for a given service, the new configuration is indicated on the MCCH one modification period in advance in the MBMS Modified services Information message indicating that the UE shall acquire information for the configuration of the PtM radio bearer, so that UEs can receive the reconfigured channel from the beginning. Thus, there is a delay between the configuration taken into account by the UE and its effective use by the network.
Such a configuration protocol is illustrated at FIG. 10 for a single cell. In this case, a service starts in the current cell (the current cell is the control cell, i.e. the cell of which is taken into account the MCCH by the UE) and does not generate any configuration problem: indeed, the timing offset between the MTCH and the MCCH (due to a different Timing offset when they are mapped on different S-CCPCHs) remains the same. However, it is not clear which frame will be considered when the modification period of the MCCH is not completely aligned on the frame boundaries of the S-CCPCH carrying MTCH.
The case with an ongoing reconfiguration illustrated at FIG. 11, generates more problems. During the Modification Period 1, the PtM configuration S1 of the Service S of cell A is sent on the MCCH as unmodified service. At the same time, the service S is sent on the cell A with the configuration S1. The UTRAN wants to change the configuration from S1 to S2. Therefore, the UTRAN broadcasts the new configuration S2 of the S-CCPCH carrying service S on the MCCH during the modification period 2 as a modified service. During the modification period 2, the MTCH carrying the service S still uses the configuration S1. But at a given frame during modification period 2, the UE will start using configuration S2. In the Modification period 3 the MCCH is used to broadcast the configuration S2 as unmodified service. Thus, until the beginning of the modification period 3, the UE will use a wrong configuration for the MCCH.
In the case a reconfiguration is ongoing and a UE starts to receive the MCCH during the modification period 2 where the new configuration is broadcast on the MCCH, the UE is not able to know about the configuration of the MTCH during the current modification period. Also, the UE is not able to receive the MTCH correctly during this period.
In order to increase the coverage, a UE which is located between different cells can receive the same MBMS services from different cells at the same time, and combine the received information as shown in FIG. 9. In this case, the UE reads the MCCH from one control cell that it has selected, this cell being named the control cell in the remainder of the description.
In the background art, there is no restriction for the alignment of the MCCHs of these cells. This implies that the modification period of MCCHs of neighbouring cells (a control cell and one of its neighbouring cells for instance) can be different, and also that the start of each modification period in neighbouring cells can be different. This occurs naturally due to the clock drift of different NodeBs, e.g. one NodeB will advance faster as another NodeB.
In order to maintain synchronisation between different services of the transmission of MTCH, the clock drift between two NodeBs can in general be easily adjusted by the RNC that is responsible for the scheduling of the S-CCPCHs by inserting an empty TTI from time to time when the time difference for the latest NodeB compared to the most advanced NodeB passes above one TTI, as illustrated at FIG. 12. However, for the synchronisation of the modification periods of the MCCH there is no easy solution, since the scheduling of the MCCH transmission is related to the System frame number (SFN, broadcast on the BCH) of each cell.
If the configuration of a service in a neighbouring cell changes, this change is aligned with the modification period of the MCCH of this neighbouring cell. However, the modification period of the neighbouring cell will not necessarily be aligned with the modification period of the cell that the UE is currently reading the MCCH from. This means that in the case the UE receives the information on the change of the configuration of a service of a neighbouring cell, it has no means for determining when this change will become active, since the offset (and the modification period) of the neighbouring cell is not aligned.